High power, high brightness LEDs generate high heat in a very small area (e.g., 1 mm2) and this heat must be efficiently dissipated while maintaining a small package (or module) size. Further, to generate a very high flux, there may be multiple LEDs in the same package. Such LEDs are usually connected in series and/or parallel within the package.
In a common package for a high power LED, the bottom metal pad of the LED die is soldered to a top metal pad of a thermally conductive submount (e.g., a ceramic), and the LED die is encapsulated. The external submount metal pads (electrically connected to the anode and cathode of the LED die) are then soldered to pads of a printed circuit board (PCB), where the PCB helps sink heat from the LED and provides power to the LED die. The LED's thermal coupling to the submount and PCB is not as good as a thermal coupling directly to a metal heat sink. When there are multiple LEDs in a single package connected in series, the thermal design is more complex since the LEDs cannot share a large metal pad for spreading heat.
This problem of heat dissipation is especially severe in the field of automobile headlights, where multiple high power LEDs must deliver high flux in a small space near a focal point in an enclosed headlight parabolic reflector.
Various prior art LED modules have been proposed for packaging multiple LEDs but there are still problems with heat sinking and size that make the packages unsuitable for an automobile headlight. Examples of this prior art include U.S. Pat. Nos. 7,806,560; 8,371,723; 2013/0005055; and 2008/0074871.
Therefore, what is needed is a technique for forming an LED module that has a relatively small size, has excellent heat sinking capability, and can contain an array of high power LEDs that may be used in automobile applications, such as headlights, indicator lights, or taillights.